As people communicate more and more using data networks, each time with more sophisticated applications, more network bandwidth is required to sustain efficiently and reliably the increasing demand for such communication and applications. As network bandwidth increases, new systems and components need to be developed and deployed, often requiring more powerful equipment that consumes more energy.
Environmental concerns are being addressed more than ever before in the electronic world, and so new building practices are gaining popularity, or at least, some interest. Among other aspects of network building practices, the system cooling and the electronic interconnect technologies bring interesting solutions/alternatives to the environmental challenge facing electronic system manufacturers.
In regard to cooling technologies used to extract heat generated by network systems, there exist several techniques, such as fans, radiators, liquid cooling, etc. Fans and radiators are commonly used due to their relatively low cost and other advantages, but they also suffer from disadvantages, such as noise, large space, environment dependence, etc. In fact, more and more problems related to noise generated by networking systems are being observed.
In addition, motherboards and other printed circuit boards (PCBs) that carry powerful digital signal processors and electronic circuits can require large radiators and/or fans attached directly to the processors and circuits. A “motherboard” is typically the main PCB in a device and is a slotted PCB upon which other PCBs (“daughter boards”) can be mounted. As a result, a board can become thicker or taller, and not as space-efficient. Obtaining suitable air flow within a system chassis containing such boards can become an important challenge for a designer. As electronic equipment and boards “upgrade” from a blade form factor to a pizza-box form factor, the equipment's cooling air flow can have to be reconsidered or even replaced by liquid cooling.
It is common today to see copper traces between electronic components to carry information (hence the name, “printed circuit” board). Boards with copper traces will find it increasingly difficult to keep up with the increasing demand for low-power devices with higher-bandwidth communication. A possible solution may come from the use of optical components to carry signals between electronic components on a board and between boards. Copper interconnects require more power than optical interconnects for the same distance, and also require more copper traces to provide the same bandwidth. In short, using more and more optical components on boards and in system designs will make systems more energy efficient, more bandwidth capable, and probably easier to build, as less physical copper layers are required per electronic board.
U.S. Pat. No. 7,699,538 to Hayase et al. describes interconnecting electronic devices on a PCB with optical fibers and connectors, and enclosing all of them in a case having a shielding member (i.e., a cover) and a sealing member (i.e., a gasket). A liquid coolant flows on top of the PCB, contained by the shielding member and the sealing member and bathing the optical elements and other components on the PCB.
U.S. Patent Application Publication No. US 2009/0193652 by Salmon describes stacking several copper substrate modules and providing cooling channels between the stacked modules. Optical fibers pass perpendicularly through the modules.
Nevertheless, there are limitations on carrying optical signals between electronic components, especially related to the way the signals are carried. Typically, light needs a fiber optic bearer to carry the signals, such as a polymer that can be placed within a backplane of a electronic chassis. A “backplane” is typically a PCB having slots into which other PCBs, or blades or cards, are plugged, and is typically just a connector without many active components on it. While those technologies exist, they are still limited at least in that each connector introduces a significant signal loss and the polymer medium degrades the signal significantly over large distances, due also to important signal loss as a function of propagation distance.
Free-space optical bearers are being developed that may help minimize the energy required to transmit signals between electronic components while also avoiding connectors to interconnect different components.
U.S. Patent Application Publication No. US 2010/0028018 by Tan et al. for “Free-Space Optical Interconnect With Asymmetric Light Pipes” describes an optical interconnect system that includes components such as circuit boards, server blades, or a backplane with respective light pipes for an optical signal. The light pipe in a component transmitting the optical signal receives a collimated beam and directs the collimated beam for transmission. The light pipe in a receiving component is nominally aligned with the light pipe of the transmitting component and separated from the first light pipe by free space. The light pipe on the receiving side is larger than the light pipe on the transmitting side and can accommodate alignment error.
U.S. Patent Application Publication No. US 2009/0274467 by Morris et al. for “Free-space Photonic Connection Using Wavelength Division Multiplexing And Optical Antenna” describes an interconnect system having an optical transmitter mounted on a first circuit board and an optical receiver mounted on a second circuit board. The optical receiver can be nominally aligned to receive an optical signal through free space from the optical transmitter. The optical receiver includes one or more light detectors, and an optical antenna coupled to direct incident light into the one or more light detectors.
A free-space optical bearer on a PCB and/or a backplane would usually require a thick and rigid PCB or backplane. While it is possible to build a thick and rigid PCB or backplane, it is extremely difficult to use such technology in equipment such as chassis blades because of the space it requires. Thus, there is a need for improved electronic assemblies and backplanes.